The detailed conformation of RNA within the ribosomal subunit and the role of the folded RNA in specific functions of the ribosome are not yet well characterized. This project is designed to localize specific sequences of RNA that occur on the surface of each ribosomal subunit of E. coli, using immunoelectron microscopy. Oligodeoxynucleotides, 8-12 nucleotides long and complementary to specific sequences within the ribosomal RNA, will be synthesized and modified to include an immunnologically distinct marker such as 1,N6-ethenoadenosine at one end. The specificity ofoligonucleotide-subunit complex formation will be verified, and the site of oligonucleotide binding to the ribosomal subunit will be localized by immunoelectron microscopy using antibodies directed against the ethenoadenosine marker. Ribosomal RNA segments that will be localized include (in the 30S subunit) the 5'-terminus, the m-RNA binding and positioning sequence, segments proposed to be involved in subunit interaction, and other regions likely to be on the subunit surface as indicated by sensitivity to chemical modification of RNase cleavage. Similar logic will be used to identify available sequences in the large subunit, and specific oligonucleotides will again be used to place elements of the sequence within the three-dimensional structure. Other available sequences will be identified by their ability to bind oligodeoxynucleotides isolated from cloned ribosomal DNA by restriction endonuclease treatment. It is believed that considerable information on the conformation of the RNA and its contribution to ribosome structure and function in protein synthesis could result.